Patent GB-670621-A (GB)
Title: Improvements in or relating to servo systems
IPC: G05D1/08
Filed: 1948-08-21
Abstract: 670,621. Automatic control systems. SPERRY CORPORATION. Aug. 21, 1948 [Aug. 22, 1947], No. 22106/48. Class 38 (iv). In an automatic system for maintaining two variables at desired values, each variable, upon deviation, produces an alternating voltage, dependent in magnitude and phase sense on the magnitude and sense of the deviation, the two voltages being in fixed phase relationship and their resultant supplied to a common amplifier the output of which supplies one phase winding of each of two two-phase servomotors, the other phase windings of which are energized from an A.C. source in such phase relationship that one servomotor, which corrects one variable, responds only to deviation of that variable, and the other servomotor, which corrects the other variable, responds only to deviation of the other variable. In Fig. 2, a gyro vertical 41 carried by a craft or other body to be controlled is associated with a double-E type pick-off 33 rigidly attached to the craft or body. Windings 34-37 on the outer limbs of the pick-off are energized from a two-phase quadrature source 38 (see Fig. 3) and relative movement between the gyro and the craft or body alters the position of an armature 39, carried by the gyro, relative to the pick-off, thereby inducing in a winding 31, on the centre limb, an A.C. voltage dependent in phase both on the direction of the horizontal axis about which movement has occurred and on the sense of such movement, and dependent in magnitude on the extent of the movement. This voltage is applied through transformers 49, potentiometers 51, and an amplifier 52, free from phase shift, to paralleled windings 53, 56 of two twophase servomotors 54, 57. The other, reference, phase windings 55, 58 of the servomotors are supplied from a two-phase quadrature source 59 so phased in relation to source 38 that only one servomotor operates upon movement of the craft or body about one horizontal, reference, axis and only the other servomotor operates upon movement about a perpendicular horizontal, reference, axis. Upon movement about any intermediate horizontal axis both motors are operated to a degree dependent on the angular position of the axis relative to the perpendicular reference axes. Each servomotor serves to control the position of the craft or body about a different one of the reference axes to maintan a level attitude. In modifications the double-E type pick-off is replaced by a wire loop fixed to the craft or body and associated with a rotating magnetic field which may be either the stray field of the gyro rotor drive or a separate field produced either by a three-phase system of electromagnets carried by the gyro rotor casing or a two-pole permanent magnet driven by the gyro rotor. As applied to the maintenance of a pair of gimbal rings in alignment with a gyro vertical the wire loop is carried by the rings and the position of each ring is controlled by one of the servomotors. As applied to the maintenance of level flight of a flying wing type aircraft each elevon is controlled by one of the servomotors. In this case, however, the angle between the two phases of the source energizing the reference phases of the servomotors is not 90 degrees but corresponds to the angle between the axes about which the elevons individually produce movement. Specification 659,791 is referred to.